Effect of quercetin on human polymorphonuclear leukocyte lysosomal enzyme release and phospholipid metabolism

Inhibition of human non-pancreatic phospholipases A2 by retinoids and flavonoids. Mechanism of action

The interaction of retinoids and flavonoids with phospholipases A2 (PLA2) was studied to assess the mechanism of inhibition. Retinoids, such as retinal, retinol, retinoic acid and retinol acetate, and flavonoids, such as quercetin, rutin, morin and sciadopitysin, inhibit Ca2+-dependent PLA2 activity of human synovial fluid (HSF) in vitro in a dose-dependent fashion; ID20S ranged from 2-8 microM. Retinal inhibited neutral active Ca2+-dependent PLA2S from human platelets, human plasma, human polymorphonuclear leukocytes and Naja mossambica mossambica venom in a dose-dependent manner while quercetin inhibits extracellular PLA2 activities of human plasma, HSF and N. m. mossambica venom in a dose-dependent manner but not PLA2 activity derived from human platelets and polymorphomonuclear leukocytes. Inhibition of PLA2 activity by both flavonoid and retinoids were independent of Ca2+ or Na+. Increasing substrate concentration (9-144 nmols) relieved the inhibition of HSF-PLA2 activity by quercetin indicating probable interaction with the substrate. The inhibition by retinal is independent of substrate concentration suggesting that inhibition by retinal is probably due to direct interaction with the enzyme. both retinal and quercetin quenched the relative fluorescent intensity of N. m. mossambica PLA2 and in a dose-dependent manner in the same concentration range at which they inhibit in vitro PLA2 activity. Retinal and quercetin shift the thermotropic phase transition of distearoylphosphatidylethanolamine (DSPE) liposomes. Both compounds broadened the transition peak, shifted the Tm to lower temperature, and decreased enthalpy significantly. These findings indicate that inhibition of non-pancreatic human PLA2S by retinoids and flavonoids can be mediated by interaction with enzyme and/or substrate.

The nutritional incidence of flavonoids: some physiological and metabolic considerations

Examination of the physiological activity of flavonoids in relation to their antiscorbutic properties shows that some of these compounds, the flavan-3-ols, have a particular nutritional impact and consequently should be distinguished from the rest of the flavonoids and polyphenols. Therefore, the use of the term 'Vitamin P' and 'Bioflavonoids' is also discussed.

Effects of silybin on histamine release from human basophil leucocytes

1. Effects of a naturally occurring flavonoid, silybin, on histamine release from human basophils were examined, in order to assess the potential utility in the treatment of allergic disorders. 2. The f-met peptide and anti-IgE-induced histamine release was significantly (P less than 0.05) inhibited in a concentration-dependent fashion. Conversely, no significant (P greater than 0.05) effect on calcium ionophore A23187-induced histamine secretion was documented. The inhibitory activity was significantly (P less than 0.05) reversed by elevating extracellular calcium concentrations. 3. The anti-allergic properties of silybin can be reasonably ascribed to a membrane-stabilizing activity, possibly related to an interference in calcium influx. These results indicate that an in vivo evaluation of the anti-allergic activity of silybin would be worthwhile.

Effect of antiperoxidative drugs on gastric damage induced by ethanol in rats

Lesion formation due to oral administration of absolute ethanol could be prevented by parenteral pretreatment with antiperoxidative drugs such as butylated hydroxytoluene (BHT), quercetin and quinacrine. Also effective were allopurinol and oxypurinol, inhibitors of xanthine oxidase, but not superoxide dismutase (SOD) and hydroxyl radical scavengers, such as sodium benzoate and dimethyl sulfoxide (DMSO). BHT, quercetin, quinacrine and sulfhydryl compounds such as reduced glutathione and cysteamine which offer gastroprotection in vivo against ethanol inhibited lipid peroxidation induced in vitro by ferrous ion in porcine gastric mucosal homogenate, but SOD, sodium benzoate, DMSO, allopurinol and oxypurinol did not. These results suggest the possibility that an active species, probably derived from free iron mobilized by the xanthine oxidase system, other than oxygen radicals such as hydroxyl radicals, contributes to lipid peroxidation and lesion formation in the gastric mucosa after absolute ethanol administration.

Effects of flavonoids on enzyme secretion and endocytosis in normal and mucolipidosis II fibroblasts

The effect of flavonoids on beta-hexosaminidase transport and endocytosis has been studied in cultured human skin fibroblasts. In mucolipidosis II fibroblast cultures, characterized by their preferential secretion of most newly synthesized hydrolases, quercetin and phloretin (200 microM) inhibited beta-hexosaminidase synthesis as well as total culture-associated enzyme activity. Taxifolin induced a 2.4-fold increase in the total enzyme activity without altering the intra- and extracellular distribution of the enzyme. Rutin, although less effective, also stimulated an overall increase in total enzyme. The flavonoid effects were all concentration-dependent. Very little effect was observed in either the distribution or the total beta-hexosaminidase activity in normal fibroblast cultures. Taxifolin and hesperitin inhibited receptor-mediated endocytosis of beta-hexosaminidase by fibroblasts up to 50% of control uptake. Naringin, quercetin, and phloretin moderately inhibited uptake by 30% while rutin and fisetin had no effect. The results demonstrate that certain naturally occurring flavonoids affect the secretion of lysosomal enzymes as well as their endocytosis by fibroblasts. Since most individuals ingest up to one gram per day of these substances, flavonoids may prove to have significant effects on normal lysosomal enzyme physiology.

Flavonoid inhibition of human basophil histamine release stimulated by various agents

Eleven naturally occurring flavonoids representing five different chemical classes were studied for their effects on human basophil histamine release triggered by six different stimuli. The flavonoids included flavone, quercetin, taxifolin, chalcone, apigenin, fisetin, rutin, phloretin, tangeretin, hesperetin, and naringin. The stimuli were antigen, anti-IgE, concanavalin A, ionophore A23187, formylmethionylleucylphenylalanine, and tetradecanoyl phorbol acetate. Concentration-effect relationships were established for each flavonoid (5-50 microM) at concentrations of stimuli which produced near optimal histamine release. Variable degrees of inhibition were noted depending on the nature of the stimulus and flavonoid structure. The flavonols, quercetin and fisetin, and the flavone, apigenin, exhibited a predilection to inhibit histamine release stimulated by IgE-dependent ligands (antigen, anti-IgE, and con A). The flavanone derivatives, taxifolin and hesperetin, were inactive, as were the glycosides, rutin and naringin. The open chain congeners, chalcone and phloretin, also possessed inhibitory activity. Thus, the flavonoids may be useful probes in comparative analysis of secretory phenomena. The findings suggest that the biochemical pathways leading to secretion differ subtly from one stimulus to another. The differences are detectable with flavonoids of different structures and possibly reflect distinct pathways of Ca2+ mobilization or other unique mechanisms of action.

Flavonoid modulation of human neutrophil function

Flavonoids are naturally occurring plant compounds that have been demonstrated to possess a variety of anti-inflammatory effects. We studied the effects of flavonoids on three aspects of neutrophil function that are commonly considered to be associated with inflammation: the release of lysosomal enzymes, the chemiluminescence (CL) response, and the production of superoxide anion. Quercetin and eight other flavonoids at a 10(-5)M concentration inhibited the neutrophil CL response to opsonized zymosan particles by approximately 60% or more. In contrast, the release of lysosomal beta-glucuronidase from neutrophils stimulated with opsonized zymosan was only inhibited by two flavonoids, quercetin and chalcone, and only at concentrations of 1.5 X 10(-4)M to 2 X 10(-4)M. Quercetin also inhibited the generation of superoxide anion by neutrophils but to a lesser degree than its effect on CL. The present studies demonstrated that certain flavonoids are not uniformly active in inhibiting neutrophil CL, beta-glucuronidase release, or superoxide generation. The effects of flavonoids on neutrophil functions probably depend on many variables including the response measured, the activating stimulus, and specific flavonoid structural features.

Comparison of the effects of quercetin with those of other flavonoids on the generation and effector function of cytotoxic T lymphocytes

In previous studies (Schwartz et al., 1982) we showed that the naturally occurring plant flavonoid quercetin can inhibit both the in vitro generation and effector function of alloantigen specific cytotoxic T lymphocytes (CTL). In the present studies, several additional flavonoids of different chemical classes were tested similarly to determine whether structure-function relationships exist. We have found that some other flavonoids, e.g. apigenin , fisetin , hesperetin and chalcone also can inhibit both CTL generation and effector function, with the effective concentration varying with the specific flavonoid tested. On the other hand, flavonoids such as rutin, naringin and catechin were inactive in both systems. Taxifolin ( dihydroquercetin ) differed from all the other flavonoids in that it was a relatively active inhibitor of CTL generation, but was essentially unable to inhibit CTL effector function. The presence of a double bond at position C-2-3 in the flavone and flavonol aglycones, a keto group at C-4, B ring hydroxylation and/or a free hydroxyl group at C-3 may be associated with activity. We also show that the effects of some, but not all, of the flavonoids active in our systems can be blocked by Cu2+ ions. Therefore, chelation of divalent cations such as Cu2+ cannot explain the function of all flavonoids in these systems.

The effect of some flavone drugs on the conversion of prostacyclin to 6-oxoprostaglandin E1

Flavonoid drugs (rutin, naringenin and quercetin) were compared with indomethacin and sulphasalazine as inhibitors of rat and rabbit renal 9-hydroxyprostaglandin dehydrogenase, prostaglandin synthesis (bovine seminal vesicle microsomes) and inactivation (rabbit colon 100,000 g supernatant), vascular PGI2 formation (rat aortic rings) and for effects on platelet aggregation and on the isolated rat stomach strip. Rutin and naringenin potently inhibited rabbit renal conversion of PGI2 and PGF2 alpha to 6-oxoPGE1 and PGE2, respectively, but had no effect on rat renal 9-hydroxyprostaglandin dehydrogenase activity, prostaglandin breakdown, vascular PGI2 synthesis, platelet aggregation or the anti-aggregatory effect of PGI2 and 6-oxoPGE1. High concentrations (100 microM) of both drugs inhibited the spasmogenic effect of PGI2 on the rat stomach strip. Naringenin and quercetin (1 mM) inhibited whilst rutin (1 mM) stimulated microsomal prostaglandin synthesis. These results suggest that rutin and naringenin may be useful experimental tools to study the biological roles of 6-oxoPGE1.